The invention relates to a multiple rotary drive system for a textile-working machine, for example, and a sewing machine, for more-specific example.
In a number of different textile-working machines, such as knitting machines or sewing machines, for example, two or more shafts which, in some cases, are very close together, have to be driven in coordination with one another but must be controllable independently of one another. One way of doing this would be to use an electric motor, and a stepper or a pulse-driven DC motor, more particularly, for rotating each shaft with electric pulse devices for coordinating the motors and, hence, the rotation of the individual shafts. For example, a pulse-emitting device on a first shaft could emit pulses in dependence upon the rotary speed the shaft, which thus assumes the character of a master shaft, to provide the basis for control of the rest of the shafts, which thus assume the character of slave shafts, with relative speed differences between any of the shafts produced electronically by frequency dividers or pulse-width changers, for example. Such solutions involving several independent electric motors operated in coordination are, however, technically complex and also require a relatively large amount of space, especially if it is necessary to provide each motor with additional equipment, such as cooling systems and the like.
U.S. Pat. No. 4,549,491 discloses another multiple-shaft rotary drive for a stitch group sewing machine.
U.S. Pat. No. 4,556,132 discloses a rotary drive for a sewing machine. It has an electric motor continuously operating at constant speed and a clutch-brake unit to produce a driving connection between the driving shaft of the electric motor and a driven shaft of the sewing machine by selective excitation of clutch or brake coils of the clutch-brake unit. On account of the extremely advantageous characteristics of this or similar drive systems, which are also developed technically to a high degree, it might appear desirable to drive plural shafts with a corresponding number of independent drives of this kind, but this would involve considerable cost and, in many applications, would be infeasibly large for the limited amount of available space.
German Utility Model Publication No. 83 30 328 discloses a buttonhole sewing machine having an electric motor driving a clutch-brake unit. The driven shaft of the clutch-brake unit is connected to two electromagnetic clutches, one of which produces a driving connection to an upper, sewing-instrumentality shaft of the sewing machine and the other, a driving connection for moving a feed dog. By actuating the latter clutch, the feed dog can be brought quickly into position before and after the actual sewing, and by actuating the former clutch, the sewing is produced while the feed dog is driven in the conventional manner, the latter clutch not being engaged in this phase.
U.S. Pat. No. 4,274,522 discloses a machine having a low-speed auxiliary motor in addition to a high-speed main motor. By an electromagnetic clutch and auxiliary V-belt, the auxiliary motor can be used to drive the main shaft otherwise driven by the main motor whenever the machine is to be driven by the low-speed auxiliary motor instead of the high-speed main motor for certain operations.